The present invention relates to a gas turbine system for conducting speed control of a generator by using a power conversion apparatus, and relates to its control method.
As an example of a conventional technique for conducting speed control of a generator by using a power conversion apparatus, JP-A-2000-345952 can be mentioned. It relates to wind power generation. A power command value of the power conversion apparatus is computed from the wind velocity. The revolution speed of a generator driven and rotated by a windmill is controlled by pitch control.
In JP-A-9-289776, there is disclosed a technique of computing a speed command of a gas turbine on the basis of an AC load power, controlling a turbine input on the basis of a result of the computation, and thereby regulating a speed of a generator.
In JP-A-11-356097, there is disclosed a technique of providing a speed proportion control section in a fuel control loop, keeping the exhaust gas temperature of a turbine engine at a fixed value, and controlling the gas turbine engine efficiently and stably.
In the technique disclosed in JP-A-2000-345952 among the conventional techniques, however, speed control is not conducted by control of a power conversion apparatus. In the case where the technique is used in a power conversion apparatus for gas turbine, therefore, the revolution speed is controlled by a mechanical variable such as a fuel flow rate, resulting in slow control. Furthermore, control of the revolution speed using fuel control of the turbine cannot exercise control so as to achieve an optimum revolution speed for the fuel flow rate by itself, resulting in a lowered efficiency.
In the techniques disclosed in JP-A-9-289776 and JP-A-11-356097, the speed of a generator is controlled by controlling a fuel flow rate to a gas turbine. In this case as well, therefore, the revolution speed is controlled by a mechanical variable. In the same way as the technique of JP-A2000-345952, therefore, the control becomes slow and the efficiency is also lowered.
An object of the present invention is to provide a gas turbine system and its control method that make it possible to prevent the control from becoming slow and achieve high efficiency running.
In order to achieve the object, in accordance with an aspect of the present invention, in a gas turbine system including: first power conversion means for converting an AC voltage of a power system to a DC voltage; second power conversion means for converting the DC voltage output from the first power conversion means into an AC voltage; a generator connected to an AC output side of the second power conversion means and driven and rotated by a gas turbine; and turbine control means for outputting a revolution speed command value depending upon a fuel flow rate of the gas turbine, the gas turbine system includes: revolution speed detection means for detecting a revolution speed of the generator; DC voltage detection means for detecting a voltage of a DC side of the first power conversion means; DC voltage command value generation means for generating a DC voltage command value in accordance with a difference between the revolution speed detected by the revolution speed detection means and the revolution speed command value output by the turbine control means; DC voltage command value selection means for selecting either a preset DC voltage command value or the DC voltage command value generated by the DC voltage command value generation means in accordance with the revolution speed detected by the DC voltage detection means; and first control means for controlling a conversion output of the first power conversion means in accordance with a control signal for making the DC voltage detected by the DC voltage detection means coincide with the DC voltage command value selected by the DC voltage command value selection means.
With the configuration, there are no mechanical variables. Accordingly, the control is prevented from being delayed and it becomes possible to run the system at a high efficiency.
In accordance with another aspect of the present invention, the gas turbine system further includes: DC current command value generation means for generating a DC voltage command value in accordance with a difference between the revolution speed detected by the revolution speed detection means and the revolution speed command value output by the turbine control means; running command selection means for selecting either a PWM running command or a diode running command in accordance with the revolution speed detected by the revolution speed detection means; and second control means for controlling a conversion output of the second power conversion means in accordance with the DC voltage command value and the running command selected by the running command selection means. In this case, the running command selection means selects diode rectification running when the detected revolution speed is at least a revolution speed at which such a DC voltage that control on the power system is possible is obtained. The running command selection means selects PWM running when the detected revolution speed is less than the revolution speed at which such a DC voltage that control on the power system is possible is obtained.
In accordance with another aspect of the present invention, in a power conversion apparatus including: first power conversion means for converting an AC voltage of a power system to a DC voltage; and second power conversion means for converting the DC voltage output from the first power conversion means into an AC voltage, a generator driven and rotated by a gas turbine being connected to an AC output side of the second power conversion means, the power conversion apparatus includes: revolution speed detection means for detecting a revolution speed of the generator; DC voltage detection means for detecting a voltage of a DC side of the first power conversion means; DC voltage command value generation means for generating a DC voltage command value in accordance with a difference between the revolution speed detected by the revolution speed detection means and a revolution speed command value depending upon a fuel flow rate of the gas turbine; DC voltage command value selection means for selecting either a preset DC voltage command value or the DC voltage command value generated by the DC voltage command value generation means in accordance with the revolution speed detected by the DC voltage detection means; and first control means for controlling a conversion output of the first power conversion means in accordance with a control signal for making the DC voltage detected by the DC voltage detection means coincide with the DC voltage command value selected by the DC voltage command value selection means.
In accordance with another aspect of the present invention, in a control method of a gas turbine system including: first power conversion means for converting an AC voltage of a power system to a DC voltage; second power conversion means for converting the DC voltage output from the first power conversion means into an AC voltage; a generator connected to an AC output side of the second power conversion means and driven and rotated by a gas turbine; and turbine control means for outputting a revolution speed command value depending upon a fuel flow rate of the gas turbine, the gas turbine system control method includes the steps of: providing revolution speed detection means for detecting a revolution speed of the generator, and DC voltage detection means for detecting a voltage of a DC side of the first power conversion means; generating a DC voltage command value in accordance with a difference between the revolution speed detected by the revolution speed detection means and the revolution speed command value output by the turbine control means; selecting either a preset DC voltage command value or the generated DC voltage command value in accordance with the revolution speed detected by the DC voltage detection means; and controlling a conversion output of the first power conversion means in accordance with a control signal for making the DC voltage detected by the DC voltage detection means coincide with the selected DC voltage command value.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.